The packaging of food articles such as poultry, fresh red meat, and processed meat products requires tough, puncture resistant, yet flexible, film materials. It is also desirable that the film materials be suitable for use in fabricating bags for packaging such food articles by the shrink wrapping method. Generally, the shrink wrapping method is predicated upon the heat-shrinking property of the bag by placing a given food article or articles into the bag, and thereafter exposing the bag to a heat source such as a flow of hot air, infrared radiation, hot water, and the like, thereby causing the bag to shrink and come into intimate contact with the contours of the food article or articles. The packaged article prepared by this packaging method has an attractive appearance which adds to the commodity value of the wrapped article, its contents are kept in a hygienic condition, and it allows shoppers to examine the quality of the contents of the packaged article.
For example, in commercial poultry packaging operations, monolayer films made from polyethylene or ethylene-vinyl acetate copolymers, and multilayer films containing ethylene-vinyl acetate copolymers are utilized extensively. Likewise, in the packaging of fresh red meat and processed meat products, multilayer heat-shrinkable films containing ethylene-vinyl acetate copolymers in one or more layers of the films are commonly employed. Ethylene-vinyl acetate copolymers have been commonly employed in such applications because of their toughness and low temperature shrinking characteristics. However, film materials in one or more film layers which possess the shrinking characteristics of ethylene-vinyl acetate copolymers and which provide additional toughness are generally very expensive materials, such as ionomers or polyurethanes. Even tougher film materials are desired for varied packaging applications, but heretofore they have not been available.
In providing such film materials, however, it must be remembered that the film material must be stretchable in order to provide a shrinkable film that will heat-shrink within a specified range of percentages, e.g., from about 30 to 50 percent at 90.degree. C. in both the machine and the transverse directions. Further, the film must be heat sealable in order to be able to fabricate bags from the film, and the heat sealed seams must not pull apart during the heat shrinking operation. In addition, the film must resist puncturing by sharp edges, such as bone edges, during the heat-shrinking operation; and there must be adequate adhesion between the several layers of a multilayer film so that delamination does not occur, either during the heat-shrinking operation, or during exposure of the film to the relatively high temperatures that may be reached during shipping and storage of the film in the summertime.
Accordingly, although the known films meet many of the requirements for packaging applications, the need still exists for improved heat-shrinkable films and bags fabricated therefrom.